Ihor Radchenko <yanta...@posteo.net> writes:
> Robert Horn <rjh...@panix.com> writes: > >>> 1. Time (YYYY-MM-DD HH:MM) not continuous and may change arbitrarily at >>> certain times a year or in future or in the past: >>> - DST transitions are not stable and change from year to year >>> according to strange rules that may involve Julian dates or >>> counting weekdays >>> - DST transition rules may change over time >>> - The new year day itself is not necessarily fixed (England >>> - Julian/Gregorian transitions happened at different times in >>> different countries >> >> Note that as a result "time when it happened" has different rules than >> "future time when it is scheduled". There are lots of other times that are >> scheduled as "future local time, subject to changing DST rules". This >> is particularly tricky for repeating times for regularly scheduled events. > > Not really. Countries may change DST at any moment in future. Or decide > to switch calendars (consider countries near the day transition line). > > And "past local time, according to the DST rules in effect at the time" > is also an option that might be useful in certain scenarios. > The issue is clarity of the expected rules for the format. If I schedule a meeting for 10:05 DST, but the rules change so that it is not DST at that location at that time in the future, what is the expected interpretation? It could be: a) the meeting should be at 10:05 ST, because the intent was to meet at 10AM in the then local time. b) the meeting should be at 11:05 ST, because the time was chosen to correspond to a particular sun angle. Getting the rules and explanation clear is the issue. It's a mistake that a great many people make with scheduling meetings. Those two behaviors need different encodings because they behave differently. -- Robert Horn rjh...@alum.mit.edu